The ring-back signal is generally not generated by the called telephone device itself but by the receiving party telephone or servicing switch. In recent years personalized ring-back signals have become popular. The called party can, for example by sending an SMS (short message service) or USSD (unstructured supplementary service data), to the servicing switch request configuration of such a personalized ring-back signal. Then the calling party will hear and/or see this personalized ring-back signal when calling the called party before the called party answers the call. Ring-back signals may include music, videos, messages, and further special effects. In addition, the called part may define specific calling parties to which the personalized ring-back signals will be played while other calling parties will receive the “traditional”, non-personalized ring-back signals (see http://en.wickipedia.org/wiki/ringback_tone).
While the called party can request configuration of a new personalized ring-back signal, it usually does not have the instruments to check if a calling party actually hears and/or sees the new configured ring-back signal.